Arsenal faces defensive injury crisis as Laurent Koscielny emerges as a doubt for Champions League clash with Olympiakos

French defender picks up knock in training and leaves Wenger with major selection headache with Vermaelen and Djourou also sidelined, raising prospect of Alex Song at center-half
Arsenal is facing a defensive crisis ahead of its Champions League tie against Olympiakos on Wednesday night, has learned.

Laurent Koscielny is a major doubt after picking up an injury in training on Monday and is not expected to recover in time to take his part in Arsenal's starting lineup at Emirates Stadium.

If Koscielny, who has started the last three Premier League and Champions League matches alongside new signing Per Mertesacker in central defense, misses out, Wenger might have to reshuffle his midfield and drop Alex Song back into defense.

Johan Djourou suffered a hamstring injury in the League Cup win over Shrewsbury last week, Sebastien Squillaci has only just returned to training after a spell on the sidelines, while rookie center-half Ignasi Miquel pulled out of the reserve team win over Blackburn Rovers on Monday night after suffering an injury in the warmup. Thomas Vermaelen is not expected to return to training until after the international break.

Wenger's only option might be to play one of his regulars out of position, with Song possibly dropping back to take on the center-half role that he has played on a few occasions for Arsenal in the past. This could mean one of the two teenagers Emmanuel Frimpong or Francis Coquelin pairing up with Mikel Arteta in central midfield.

One boost for Wenger is that Theo Walcott is expected to be available for selection, despite reports to the contrary at the weekend. The England forward picked up an injury in the 3-0 victory over Bolton on Saturday, but scans on his knee and hamstring revealed no serious damage.

Follow Wayne Veysey on